This invention relates to dynamoelectric machines and more particularly to a brushholder and technique which facilitates automated assembly of such machines.
The brush riggings for motors, generators and the like vary in design, but in general consist of boxes to house the brushes, a spring means to apply pressure to the brushes to urge them against a commutator, connecting electrical leads to provide a current path to the brushes and a mounting surface to secure these elements as well as to provide some means to secure the entire assembly to the motor in such a manner as to place the brushes in a proper working relationship with the commutator.
One of the most popular designs, especially for small fractional horsepower motors, is to utilize a molded brushcard member of one-piece construction formed from a high temperature resistant plastic which is electrically nonconductive. The member has the brush boxes formed thereon as well as various openings for securing it to the motor housing and for receiving an extended armature shaft and the commutator secured to the shaft.
The prior riggings present problems when they are contemplated for use in an automated assembly process. In particular, while assembling the armature in a motor, complicated movements would have to be performed by the automation equipment to hold the brushes back in the brush box against the pressure being applied to the brushes by the spring means until such time as the commutator is positioned to receive the brushes.
Although this is particularly a problem for automated assembly of motors, it also applies to those units being assembled by hand as special tools and fixtures have previously been required to hold the brushes while the armature is being assembled.
In the assembly of dynamoelectric machines of the type wherein the armature shaft is mounted in bushing bearings, various types of retainers have been utilized to secure the brushes within the brush box until the armature is assembled thereto. Exemplary brush retainers are disclosed in King, U.S. Pat. No. 4,293,789 issued Oct. 6, 1981 and the commonly owned Stewart, Sr., U.S. Pat. No. 4,694,214 issued Sept. 15, 1987 which is incorporated herein by reference. In dynamoelectric machines such as those disclosed in King and Stewart, Sr., the commutator functions to displace a brush retainer upon assembly of the brushbox to the armature. In such machines, the brush retainer need only hold back the brushes to provide an unobstructed passageway for the armature shaft and commutator until the commutator is positioned adjacent the brushes.
However, in dynamoelectric machine applications such as continuous duty motors, bearing assemblies of the rolling element type must be utilized rather than bushing mounts. In these types of machines, the bearing assembly is secured to the armature shaft before the brushcard is positioned with respect to the commutator. Consequently, the bearing assembly must also be passed through the brush rigging in positioning the brushcard. Since the diametral size of the bearing assembly may be greater than the commutator, the brush holders described in King and Stewart, Sr., cannot be utilized.
Accordingly, it is an object of the present invention to provide a new and improved brushcard subassembly which facilitates automated assembly of dynamoelectric machines having rolling element bearings.
Another object of the invention is to provide such a brushcard subassembly which facilitates automated mounting over a large bearing assembly secured to the armature shaft.
A further object of the invention is to provide such a brushcard subassembly which automatically releases the brushes to engage the commutator upon positioning the commutator within the brushcard subassembly.
Another object of the invention is to provide a new and improved method of automated assembly of dynamoelectric machines having rolling element bearings larger than the commutator.
Another object of the invention is to provide a safe, economical, easy to assemble and reliable dynamoelectric machine.
It has been found that the foregoing and related objects are attained in a dynamoelectric machine having an armature subassembly and a cooperating brushcard subassembly for mounting about the commutator of the armature subassembly. The armature includes an armature shaft, armature windings, a commutator mounted to the armature shaft adjacent the windings, and an antifriction bearing assembly mounted to the armature shaft in spaced disposition to the commutator. The bearing assembly has an outer diametral dimension greater than the commutator. The armature subassembly also includes an actuator for displacing a brush retainer on the brushcard subassembly. The actuator is mounted to the shaft between the bearing assembly and the commutator. The brushcard subassembly includes a support bracket for mounting brush holders radially adjacent the commutator with the bracket defining a central opening to receive the commutator. The central opening is dimensioned to be larger than the diametral dimension of the bearing assembly so as to permit the bearing assembly to pass therethrough. At least one brush holder is mounted to the support bracket so as to extend radially relative to the commutator in assembly. A brush is slidably mounted in the holder with a biasing spring to urge the brush into contact with the commutator. A displaceable retainer is mounted to the support bracket for retaining brushes radially outwardly so as to form an unobstructed central passageway greater than the diametral dimension of the bearing assembly to permit the bearing assembly to pass through the passageway and through the central opening of the support bracket during assembly. The retainer is releaseably mounted to the support bracket for automatic displacement by the actuator upon placement of the commutator into the central opening of the support bracket to allow the brush to engage the commutator. The retainer is a cylindrical sleeve releasably mounted within the central opening of the support bracket for axial displacement by the actuator. The actuator is a disk coaxially mounted to the armature shaft for sliding movement along the shaft responsive to engagement with the sleeve during assembly to position the disk to abut the commutator for movement therewith so that movement of the commutator into the central opening causes the disk to displace the sleeve axially from the brushcard to release the brushes so as to engage the commutator.